The Complete Aristotle (eng.)

form a single
proposition, it is plain that the first proposition either has more
than one significance or else has none; for a particular man is not
a horse.
    This, then, is another instance of those propositions of which
both the positive and the negative forms may be true or false
simultaneously.
9
    In the case of that which is or which has taken place,
propositions, whether positive or negative, must be true or false.
Again, in the case of a pair of contradictories, either when the
subject is universal and the propositions are of a universal
character, or when it is individual, as has been said,’ one of the
two must be true and the other false; whereas when the subject is
universal, but the propositions are not of a universal character,
there is no such necessity. We have discussed this type also in a
previous chapter.
    When the subject, however, is individual, and that which is
predicated of it relates to the future, the case is altered. For if
all propositions whether positive or negative are either true or
false, then any given predicate must either belong to the subject
or not, so that if one man affirms that an event of a given
character will take place and another denies it, it is plain that
the statement of the one will correspond with reality and that of
the other will not. For the predicate cannot both belong and not
belong to the subject at one and the same time with regard to the
future.
    Thus, if it is true to say that a thing is white, it must
necessarily be white; if the reverse proposition is true, it will
of necessity not be white. Again, if it is white, the proposition
stating that it is white was true; if it is not white, the
proposition to the opposite effect was true. And if it is not
white, the man who states that it is making a false statement; and
if the man who states that it is white is making a false statement,
it follows that it is not white. It may therefore be argued that it
is necessary that affirmations or denials must be either true or
false.
    Now if this be so, nothing is or takes place fortuitously,
either in the present or in the future, and there are no real
alternatives; everything takes place of necessity and is fixed. For
either he that affirms that it will take place or he that denies
this is in correspondence with fact, whereas if things did not take
place of necessity, an event might just as easily not happen as
happen; for the meaning of the word ‘fortuitous’ with regard to
present or future events is that reality is so constituted that it
may issue in either of two opposite directions. Again, if a thing
is white now, it was true before to say that it would be white, so
that of anything that has taken place it was always true to say ‘it
is’ or ‘it will be’. But if it was always true to say that a thing
is or will be, it is not possible that it should not be or not be
about to be, and when a thing cannot not come to be, it is
impossible that it should not come to be, and when it is impossible
that it should not come to be, it must come to be. All, then, that
is about to be must of necessity take place. It results from this
that nothing is uncertain or fortuitous, for if it were fortuitous
it would not be necessary.
    Again, to say that neither the affirmation nor the denial is
true, maintaining, let us say, that an event neither will take
place nor will not take place, is to take up a position impossible
to defend. In the first place, though facts should prove the one
proposition false, the opposite would still be untrue. Secondly, if
it was true to say that a thing was both white and large, both
these qualities must necessarily belong to it; and if they will
belong to it the next day, they must necessarily belong to it the
next day. But if an event is neither to take place nor not to take
place the next day, the element of chance will be eliminated. For
example, it would be necessary that a sea-fight should neither take
place nor fail to take place on the next day.
    These awkward results and others of the same kind follow, if it
is an irrefragable law that of every pair of contradictory
propositions, whether they have regard to universals and are stated
as universally applicable, or whether they have regard to
individuals, one must be true and the other false, and that there
are no real alternatives, but that all that is or takes place is
the outcome of necessity. There would be no need to deliberate or
to take trouble, on the supposition that if we should